Have any of your doctors dicussed treating your tachycardia with medicine? Tachycardia is defined as "pathological rapid heart rate". Sometimes I think it can be termed ideopathic, meaning unknown origin of the cause. I have read that there are many causes of tachycardia. Medicines (otc and prescription), tobacco, alcohol, endocrine gland disorders, benign adrenalin gland tumors etc. You don't smoke or drink, so there are many more things to rule out. The brain (sypathetic portion of our autonomic nervous system) controls our heart rate in conjunction with the sinus nodes in our heart, and probably more things that I haven't a clue about. But, tachycardia can be treated with beta blockers and I suppose other medications. I take them and they keep my heart rate normal. They are serious meds and your doctor may not think your tachycardia is bad enough to treat, but it can be treated BEFORE a cause is found for them. Hope you get better soon and find some help and answers